1. FIELD OF THE INVENTION
This invention relates to cartridge filters for use in filter systems designed to remove solid particles or dust from large volumes of gases, including air, in which they are suspended, such as industrial sweepers, bag houses, plenum type dust collectors, and the like. These systems rely on a plurality of filter devices which embody a porous filter material through which the gaseous medium passes, the solids being retained on the upstream surface of the filter medium as the gases pass through. The separated solids build up on the upstream side of the filter medium with time and must be removed before the thickness of the accumulated solids layer causes excessive pressure drop. In current practice, the filter cake is dislodged from the filter elements by means of a pulse of compressed air admitted to the filter element, a reverse air flow, or a shaker mechanism. The filter medium flexes under the force of the air pulse to dislodge the filter cake and the flow of gases being filtered is maintained while such flexing and dislodging is taking place. The improved cartridge filter of the invention is intended for use with such devices and methods of cleaning, in particular the pulse jet cleaning method.
2. DESCRIPTION OF THE PRIOR ART
Cartridge filters per se are well known in the art for both gaseous and liquid filtration and have the usual construction of a folded or pleated filter medium arranged cylindrically around a perforated cylindrical supporting member or tube. The filter medium may be optionally surrounded by a perforated cylindrical supporting member, such as a perforated tube. The supporting tubes and filter medium are adhered to end caps which prevent leakage around the filter medium and provide support for the filter medium and the other components.
Examples of such cartridges are found in the Parker patent, U.S. Pat. No. 2,739,916, where thermoplastic resin plastisol is used to bond, seal, or pot the ends of the pleated filter medium and supporting members in a layer of resin plastisol in the end caps. Mumby, in U.S. Pat. No. 3,392,843, describes a disposable cartridge, including a paper filter medium, where the outer edges of the pleats are indented at certain points to form a surface for disposing a filter reinforcing adhesive to space adjacent pleats apart from one another to form better inlets for fluid to be filtered to the filter medium. A knock-down filter was shown by Frosolone, in U.S. Pat. No. 3,498,464, wherein a pleated paper medium was used to filter organic solvents. A dual-stage cartridge was provided by Reading, in U.S. Pat. No. 3,552,553, where a foamlike material comprised the first stage filter medium which surrounded a pleated paper or felt-like second stage filter medium. Groh, in U.S. Pat. No. 4,007,026, in filters for an industrial sweeper apparatus, utilizes a pleated paper filter surrounding a cylindrical coiled spring inner support with restraining bands around the outside of the filter medium to resist the force of the air pulse jet cleaning action on the filter medium.
A web, frame, or grid of wire supports has been used to support filter media against the pressure of a gas being filtered. Boothe, U.S. Pat. No. 3,853,529, provided in flat disposable cartridge form a pleated wire frame on the downstream side of the filter medium and coated the wires of the web with an adhesive to both protect the wire against corrosion and to bond to the filter medium to prevent its billowing in the gaps between the wires of the support frame under the pressure of the stream of air being filtered. Rudin, U.S. Pat. No. 3,933,452, also folded a filter medium and wire support frame into a bellows shape in a plastic frame cartridge. Successive folds of the wire frame and filter medium were held apart by projections from the wire frame of one fold extending across to the frame wires of the adjacent fold.
Huber and Meier, U.S. Pat. No. 3,679,537, utilized wires disposed on both sides of strips of column packing element for materials exchange columns with the wires spot welded together into a frame to hold the packing in place.
A very simple way to hold a pleated filter medium across a gas steam was provided by Giocovas, in U.S. Pat. No. 4,004,899, by bending a fiber strand (wire) into a series of parallel longitudinal portions disposed in two parallel planes connected by intervening lateral wire sections and weaving the filter medium back and forth between alternating wires disposed in the two parallel planes to give pleats supported on the inside of each apex by one of the longitudinal wires from one or the other of each of the alternating planes of wires.
The problems of support of a filter medium on both sides against gas flow pressures was addressed by Leliaert in U.S. Pat. No. 3,853,509. A filter bag was supported between inner and outer wire cages of conforming star-shaped cross-section to which the filter bag conformed. The outer support cage circumferential wires, however, also provided many locations where dust could settle or form into piles which could partially block the active filter surface and result in a more rapid pressure drop than might be otherwise desirable.
Also known to be used in the art are inner wire support cages composed of longitudinal wires which extend the length of the filter medium and disposed at the outer apex inside each fold of the filter medium, the ends of each wire being attached, usually by spot welding, to a supporting circle of wire at both top and bottom. A conforming similarly constructed outer cage is used in conjunction with the inner cage, the filter medium being sandwiched between them. U-shaped bulges extend outwardly from the longitudinal wires of the outer cage to circular circumferential wire rings to which they are welded. The outer circumferential ring supports help resist the bowing out of the outer wire supports and filter medium when air jet pulse methods of cleaning are used.